There are many factors to take into consideration when purchasing a thermostat. This guide will discuss key differences between thermostats and how to decide which thermostat is right for you. The main differences between thermostats are:

The number of stages refers to the number of heating or cooling sources that may be controlled by a single thermostat. For example, if a system contains baseboard heat, a hot air system, and air conditioning then there are two heating stages, and one cool. In this example, a thermostat that can control two heat and one cool stage should be selected. It is important to note that if you have auxiliary heat (or backup heat), that counts as a second heating source.

Number of stages may be written in several different ways. The two most common are 2H/1C or 2 Heat / 1 Cool. These mean the same thing-- that there are two sources of heat and one source of cool that may be controlled by this thermostat. Number of stages can vary from single heat or single cool all the way up to 4 Heats and 3 Cools on one thermostat. In order for the wiring to work properly, you must purchase a thermostat that accounts for the number of heating or cooling sources present in your given space.

Programmability refers to the level of control a user can have over the system. Programmable thermostats allow you to set the heating or cooling system to turn on or off at certain times of the day or on certain days of the week at different temperatures. A 7-day programmable thermostat may have a distinct time and temperature setting for each day of the week. Other common types of programmable thermostat include the 5-2 and 5-1-1 which allow one weekday setting and one (for the 5-2) or two (for the 5-1-1) separate settings for the weekend when the hours spent in that room will likely be different.

A non-programmable thermostat is settings must be manually changed for temperature and on/off functionality of heating or cooling sources.

Due to the great level of control with a programmable thermostat, these units are highly energy efficient and thus allow you to save money on heating and cooling bills. For example, if no one will be in a given space from 9am to 5pm, a programmable thermostat
can be set to turn off at 9 am and turn back on at 4.30pm so the space reaches a comfortable temperature for you to return to it. In contrast, a non-programmable thermostat may either be left on during this time period, wasting energy and money, or off, meaning that you get home to an uncomfortably hot or cold room.

Thermostats vary by the different types of heating and/or cooling applications they control. Because there are many different heating and cooling sources it is important to make sure the thermostat you purchase can operate the type of heat or cool source you will be using. For example, some thermostats can handle a heat pump system while others cannot. If you have a heat pump system, it is important to purchase a thermostat that specifically states that it can be used with a heat pump system or your thermostat will not work properly. The same logic applies for electric heat, millivolt, and other systems.

There are several manufacturers of thermostats available to consumers today. Honeywell, White Rodgers, Robertshaw, Lux, Wirsbo and Tekmar all produce high quality thermostats. While Honeywell thermostats are the most recognized and the best selling brand of thermostat, the other manufacturers are large companies who create high quality products and stand behind them.

User interface refers to the method or way in which a person interacts with their thermostat. Thermostats may be mechanical with a simple dial, digital with buttons to move the temperature up or down, or feature a touch screen. As thermostats move from mechanical to touch screen, they tend to get more complicated in terms of functionality and operation. Touch screen thermostats are relatively new, but are quickly gaining in popularity. An example of a touch screen thermostat is the Honeywell TH8110U1003.

Some thermostats offer features that are specific to that thermostat. These features may include sensors (indoor, outdoor, remote...), humidification control, and password protection. These features tend to add to the price of a thermostat. If you need one of these features, be sure to check the product description to see if it contains the given feature

Thermostats may be mounted horizontally or vertically. The difference is the orientation of the thermostat and the preference is generally either in the way the thermostat looks, or with space constraints. Several models of thermostats may be purchased in vertical or horizontal mount.

Thermostats run on either line voltage or low voltage. The easiest way to tell if you need a line or low voltage thermostat is to look at the wire. If it is a very thin wire (like a doorbell or speaker wire), you will need a low voltage thermostat. If it is a heavy wire, you will need a line voltage thermostat.

Thermostats may feature automatic changeover or manual changeover. Changeover refers to the thermostat being switched from heat to cool as the air crosses a certain temperature. Auto changeover thermostats switch from heat to cool automatically while manual changeover thermostats must be changed by hand.